Nozzle structure for hydrogen gas burner apparatus

ABSTRACT

The present disclosure provides a nozzle structure for a hydrogen gas burner apparatus capable of reducing an amount of generated NOx. A nozzle structure for a hydrogen gas burner apparatus includes an outer tube and an inner tube concentrically disposed inside the outer tube. The inner tube is disposed so that an oxygen-containing gas is discharged from an opened end of the inner tube in an axial direction of the inner tube. The outer tube extends beyond the opened end of the inner tube in the axial direction of the inner tube so that a hydrogen gas passes through a space between an inner circumferential surface of the outer tube and an outer circumferential surface of the inner tube.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 16/101,694 filed Aug. 13,2018, which claims priority based on Japanese patent application No.2017-169965, filed on Sep. 5, 2017, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND

The present disclosure relates to a nozzle structure for a hydrogen gasburner apparatus. Japanese Unexamined Patent Application Publication No.2005-188775 discloses a nozzle structure for a burner in which acombustion gas such as a hydrocarbon gas is premixed with air, so thatgeneration of NOx is suppressed.

SUMMARY

The present inventors have found the following problem. That is, thereare cases where a hydrogen gas is used as a fuel gas. In such a case,since the hydrogen gas is highly reactive compared to a hydrocarbon gas,a temperature of a combustion flame could locally become high. As aresult, a large amount of NOx is sometimes generated.

The present disclosure has been made to reduce an amount of generatedNOx.

A first exemplary aspect is a nozzle structure for a hydrogen gas burnerapparatus, including an outer tube and an inner tube concentricallydisposed inside the outer tube, in which

the inner tube is disposed so that an oxygen-containing gas isdischarged from an opened end of the inner tube in an axial direction(e.g., a direction along an axis Y1, a direction roughly parallel to theaxis Y1, or the like), and

the outer tube extends beyond the opened end of the inner tube in theaxial direction so that a hydrogen gas passes through a space between aninner circumferential surface of the outer tube and an outercircumferential surface of the inner tube.

According to the above-described configuration, after being dischargedfrom the opened end of the inner tube in the axial direction, theoxygen-containing gas proceeds along an inner side of a part of theouter tube that extends beyond the opened end of the inner tube in theaxial direction. Meanwhile, after passing through the space between theinner circumferential surface of the outer tube and the outercircumferential surface of the inner tube, the hydrogen gas proceedsalong an outer periphery of the oxygen-containing gas. In this way,contact between the oxygen-containing gas and the hydrogen gas issuppressed, thus making it possible to suppress mixture of theoxygen-containing gas and the hydrogen gas. Therefore, it is possible toprevent a temperature of a combustion flame from locally becoming highand thereby to reduce the amount of generated NOx.

Further, the nozzle structure may further include:

an oxygen-containing gas blowing duct configured to blow out theoxygen-containing gas in the axial direction and make theoxygen-containing gas pass through a space inside the inner tube; and

a hydrogen gas blowing duct configured to blow out the hydrogen gas intothe space between the inner circumferential surface of the outer tubeand the outer circumferential surface of the inner tube in the axialdirection, and make the hydrogen gas pass through between the innercircumferential surface of the outer tube and the outer circumferentialsurface of the inner tube, in which

the oxygen-containing gas blowing duct may have a circular shape, and

the hydrogen gas blowing duct may have an annular shape so as tosurround the oxygen-containing gas blowing duct.

According to the above-described configuration, since the hydrogen gasand the oxygen-containing gas are further propelled along the axialdirection, the progress of the mixture of the hydrogen gas and theoxygen-containing gas is further suppressed. Therefore, it is possibleto further prevent the temperature of the combustion flame from locallybecoming high and thereby to further reduce the amount of generated NOx.

Further, in a section between the opened end of the inner tube and abase part thereof, a fin that extends in the axial direction whileprotruding toward the inner tube may be provided on the innercircumferential surface of the outer tube, or a fin that extends in theaxial direction while protruding toward the outer tube may be providedon the outer circumferential surface of the inner tube.

According to the above-described configuration, since the hydrogen gasand the oxygen-containing gas are further propelled along the axialdirection, the progress of the mixture of the hydrogen gas and theoxygen-containing gas is further suppressed. Therefore, it is possibleto further prevent the temperature of the combustion flame from locallybecoming high and thereby to further reduce the amount of generated NOx.

The present disclosure can reduce the amount of generated NOx.

The above and other objects, features and advantages of the presentdisclosure will become more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a nozzle structure for a hydrogen gasburner apparatus according to a first embodiment;

FIG. 2 is a cross section of the nozzle structure for the hydrogen gasburner apparatus according to the first embodiment;

FIG. 3 is a cross section of the nozzle structure for the hydrogen gasburner apparatus according to the first embodiment;

FIG. 4 is a graph showing amounts of generated NOx versus ratios Va/Vhof air flow velocities Va and hydrogen flow velocities Vh;

FIG. 5 is a graph showing amounts of generated NOx versus air ratios;

FIG. 6 is a graph showing amounts of generated NOx versus concentrationof oxygens of an oxygen-containing gas;

FIG. 7 is a cross section of a modified example of the nozzle structurefor the hydrogen gas burner apparatus according to the first embodiment;

FIG. 8 is a cross section of a modified example of the nozzle structurefor the hydrogen gas burner apparatus according to the first embodiment;

FIG. 9 is a cross section of another modified example of the nozzlestructure for the hydrogen gas burner apparatus according to the firstembodiment;

FIG. 10 is a cross section of another modified example of the nozzlestructure for the hydrogen gas burner apparatus according to the firstembodiment; and

FIG. 11 is a graph showing amounts of generated NOx versus combustionload factors.

DESCRIPTION OF EMBODIMENTS

Specific embodiments to which the present disclosure is applied areexplained hereinafter in detail with reference to the drawings. However,the present disclosure is not limited to embodiments shown below.Further, the following descriptions and the drawings are simplified asappropriate for clarifying the explanation. A right-handedthree-dimensional xyz-coordinate system is defined in FIGS. 1-4 and7-10.

First Embodiment

A first embodiment is described with reference to FIGS. 1 to 3.

As shown in FIGS. 1 and 2, a nozzle structure 10 for a hydrogen gasburner apparatus includes an outer tube 1, an inner tube 2, and a gasblowing part 3. The nozzle structure 10 is used as a nozzle disposed ina hydrogen gas burner apparatus.

The outer tube 1 includes a cylindrical part 1 a having an axis Y1. Thecylindrical part 1 a includes an outer circumferential surface 1 e.Specifically, the cylindrical part 1 a is attached to the gas blowingpart 3 and extends from the gas blowing part 3 roughly in a straightline along the axis Y1. The outer tube 1 is made of a material thatreceives heat from the inside thereof and radiates radiant heat to theoutside. The outer tube 1 is, for example, a radiant tube.

While one end part 1 b of the outer tube 1 in the example shown in FIGS.1 and 2 is opened, the other end part 1 c is closed. Although theexample of the cylindrical part 1 a shown in FIG. 1 is a cylindricalbody extending roughly in a straight line along the axis Y1, the shapeof the cylindrical part is not limited to this example. That is, thecylindrical part may further include a cylindrical part that extendsalong a curved line. For example, the cylindrical part may furtherinclude a cylindrical part that extends along a curved line such as aU-shaped line or an M-shaped line. Further, although the other end part1 c is closed by the gas blowing part 3 in the example of the outer tube1 shown in FIGS. 1 and 2, the other end part 1 c may include an openingas required for discharging an exhaust gas.

The inner tube 2 is a cylindrical body with an opened end 2 b and anopened base-side end part 2 c. The inner tube 2 is attached to the gasblowing part 3 and concentrically disposed inside the outer tube 1.Therefore, the inner tube 2 is a cylindrical body having, like thecylindrical part 1 a of the outer tube 1, the axis Y1. Since the innertube 2 is shorter than the outer tube 1, the outer tube 1 extends beyondthe opened end 2 b of the inner tube 2 in a direction along the axis Y1.

As shown in FIG. 3, the gas blowing part 3 includes an oxygen-containinggas blowing duct 3 a for blowing out an oxygen-containing gas and ahydrogen gas blowing duct 3 b for blowing out a hydrogen gas. Examplesof gases that can be used as the oxygen-containing gas include air andmixed gases. Examples of the mixed gas include those obtained by mixingan exhaust gas and air, and nitrogen and air. The oxygen-containing gasmay be at a room temperature or may be preheated. Note that theoxygen-containing gas is not limited to air and may be any gascontaining oxygen. Further, it is preferable that the oxygen-containinggas not substantially contain hydrogen. The oxygen-containing gas may begenerated by using a manufacturing method including a process forremoving hydrogen using a publicly-known method.

The oxygen-containing gas blowing duct 3 a has a circular shape.Further, the oxygen-containing gas blowing duct 3 a blows out anoxygen-containing gas in a direction along the axis Y1 and makes theoxygen-containing gas pass through the space inside the inner tube 2.The inner tube 2 discharges the oxygen-containing gas from its openedend 2 b in the direction along the axis Y1.

The hydrogen gas blowing duct 3 b has an annular shape so as to surroundthe oxygen-containing gas blowing duct 3 a. The hydrogen gas blowingduct 3 b blows out a hydrogen gas into a space (i.e., a gap) between aninner circumferential surface 1 d of the outer tube 1 and an outercircumferential surface 2 e of the inner tube 2 in a direction roughlyparallel to the axis Y1 and makes the hydrogen gas pass through thespace between the inner circumferential surface 1 d of the outer tube 1and the outer circumferential surface 2 e of the tube 2. The outer tube1 and the inner tube 2 discharge the hydrogen gas from the opened end 2b of the inner tube 2 in the direction along the axis Y1.

(Heating Method)

Next, a heating method using the nozzle structure 10 for a hydrogen gasburner apparatus is described with reference to FIGS. 1 to 3.

As shown in FIG. 2, while a hydrogen gas is blown out from the hydrogengas blowing duct 3 b, an oxygen-containing gas is blown out from theoxygen-containing gas blowing duct 3 a.

As a result, the hydrogen gas and the oxygen-containing gas aredischarged from the opened end 2 b of the inner tube 2 in a directionroughly parallel to the axis Y1. After being discharged from the openedend 2 b of the inner tube 2 in the direction along the axis Y1, theoxygen-containing gas proceeds inside of the part of the outer tube 1that extends beyond the opened end 2 b toward the one end 1 b of theouter tube 1. Meanwhile, after passing through the space between theinner circumferential surface 1 d of the outer tube 1 and the outercircumferential surface 2 e of the inner tube 2, the hydrogen gasproceeds along the outer periphery of the oxygen-containing gas. In thisway, contact between the oxygen-containing gas and the hydrogen gas isprevented, thus making it possible to suppress the mixture of theoxygen-containing gas and the hydrogen gas.

Next, by using an ignition apparatus such as a spark plug (not shown), aspark is made and the hydrogen gas is ignited and burned. As a result, atubular flame F1 is generated. The tubular flame F1 extends from theopened end 2 b of the inner tube 2 toward the one end 1 b of the outertube 1 and converges. The tubular flame F1 heats the outer tube 1, andthe outer tube 1 generates radiant heat and thereby generates heat.

The condition for the combustion in the heating method using the nozzlestructure 10 for the hydrogen gas burner apparatus is explainedhereinafter. Amounts of generated NOx were measured under variousconditions by using an example of the heat generation method using thenozzle structure 10 for the hydrogen gas burner apparatus. FIGS. 4 to 6show results of these measurements.

As shown in FIG. 4, when a ratio Va/Vh between an air flow velocity Vaand a hydrogen flow velocity Vh is equal to or close to 1.0, the amountof generated NOx is the lowest. Therefore, the ratio Va/Vh is preferablyequal to or close to 1.0. For example, the ratio Va/Vh is preferably ina range of no lower than 0.1 and no higher than 3.0. The air flowvelocity Va and the hydrogen flow velocity Vh can be changed by changingthe inner diameter of the inner tube 2 and the thickness of the innertube 2, respectively.

Further, as shown in FIG. 5, when the air ratio is increased, the amountof generated NOx tends to increase. The air ratio is preferably in arange of no lower than 1.0 and no higher than 1.5. The air ratio ispreferably 1.0 or higher because, based on calculation, when the airratio is 1.0 or higher, no unburned hydrogen is discharged. Further, theair ratio is preferably 1.5 or lower because when the air ratio is 1.5or lower, the combustion does not require a larger amount of air, thuscontributing to energy-saving.

Further, as shown in FIG. 6, when the concentration of oxygen in theoxygen-containing gas is increased, the amount of generated NOx tends toincrease. It is preferable that the concentration of oxygen in theoxygen-containing gas be, for example, no lower than 10 vl % and nohigher than 21 vl %. The concentration of oxygen in theoxygen-containing gas is preferably 10% or higher because when theconnection is 10% or higher, a combustion flame can be stably generated.The concentration of oxygen in the oxygen-containing gas is preferablylower than 21% because when the concentration is lower than 21%, it islower than the concentration of oxygen in the air, thus making itpossible to reduce the amount of generated NOx.

As described above, after the oxygen-containing gas is discharged fromthe opened end 2 b of the inner tube 2 in the direction along the axisY1, it proceeds inside of the part of the outer tube 1 that extendsbeyond the opened end 2 b of the inner tube 2 in the direction along theaxis Y1. Meanwhile, after the hydrogen gas passes through the spacebetween the inner circumferential surface 1 d of the outer tube 1 andthe outer circumferential surface 2 e of the inner tube 2, it proceedsalong the outer periphery of the oxygen-containing gas. In this way,contact between the oxygen-containing gas and the hydrogen gas issuppressed and hence the hydrogen gas is slowly burned. Therefore, it ispossible to prevent the temperature of the tubular flame F1 from locallybecoming high and thereby to reduce the amount of generated NOx.Further, a flashback phenomenon hardly occurs.

Further, the nozzle structure 10 includes the gas blowing part 3, andthe gas blowing part 3 includes the oxygen-containing gas blowing duct 3a having a circular shape and the hydrogen gas blowing duct 3 b havingan annular shape. Since the oxygen-containing gas blowing duct 3 aenables the oxygen-containing gas to be uniformly blown out therefrom inthe direction along the axis Y1, a flow of the oxygen-containing gashaving a circular cross section is formed. Further, since the hydrogengas blowing duct 3 b enables the hydrogen gas to be uniformly blown outtherefrom in the direction roughly parallel to the axis Y1, a flow ofthe hydrogen gas having an annular cross section is formed. Therefore,the hydrogen gas having the annular cross section flows around the outerperiphery of the oxygen-containing gas having the circular crosssection. Consequently, the mixture of the hydrogen gas and theoxygen-containing gas is further prevented from advancing. Accordingly,it is possible to further prevent the temperature of the tubular flameF1 from locally becoming high and thereby to further reduce the amountof generated NOx.

Modified Example of First Embodiment

Next, a modified example of the nozzle structure according to the firstembodiment is described with reference to FIGS. 7 and 8.

As shown in FIGS. 7 and 8, a nozzle structure 20 has a configurationsimilar to that of the nozzle structure 10 (see FIGS. 1 to 3), exceptthat the nozzle structure 20 includes fins 4. The fins 4 are disposed onthe outer circumferential surface 2 e of the inner tube 2. As shown inFIG. 7, in a section between the opened end 2 b of the inner tube 2 andthe base-side end part 2 c thereof, the fins 4 extend along the axis Y1of the outer tube 1 while protruding toward the outer tube 1. As shownin FIG. 8, a plurality of fins 4 are provided on the outercircumferential surface 2 e of the inner tube 2 and are disposed in sucha manner that they perpendicularly protrude from the outercircumferential surface 2 e in a radial pattern around the axis Y1. Inthe example of the fins 4 shown in FIG. 8, twelve fins are provided onthe outer circumferential surface 2 e of the inner tube 2. In theexample of the fins 4 shown in FIG. 8, they are arranged around the axisY1 at angular intervals that are obtained by dividing 360° by twelve,i.e., arranged at intervals of 30°.

Note that the nozzle structure 20 comprises the fins 4, and the fins 4guide the hydrogen gas blown out from the hydrogen gas blowing duct 3 bso that the hydrogen gas is further propelled in a direction roughlyparallel to the axis Y1 toward the one end part 1 b of the outer tube 1.Further, the fins 4 prevent the hydrogen gas from flowing in such amanner that it is rotated around the axis Y1. Therefore, the mixture ofthe hydrogen gas and the oxygen-containing gas is further prevented fromadvancing. Consequently, it is possible to further prevent thetemperature of the tubular flame F1 from locally becoming high andthereby to further reduce the amount of generated NOx.

Another Modified Example of First Embodiment

Next, another modified example of the nozzle structure according to thefirst embodiment is described with reference to FIGS. 9 and 10.

As shown in FIGS. 9 and 10, a nozzle structure 30 has a configurationsimilar to that of the nozzle structure 10 (see FIGS. 1 to 3), exceptthat the nozzle structure 30 includes fins 5. The fins 5 are disposed onthe surface of the outer tube 1 that faces the inner tube 2, i.e.,disposed on the inner circumferential surface 1 d of the outer tube 1.As shown in FIG. 9, in a section between the opened end 2 b of the innertube 2 and the base-side end part 2 c thereof, the fins 5 extend in adirection roughly parallel to the axis Y1 of the outer tube 1 whileprotruding toward the inner tube 2. A plurality of fins 5 are providedon the inner circumferential surface 1 d of the outer tube 1 and aredisposed in such a manner that they perpendicularly protrude from theinner circumferential surface 1 d in a radial pattern around the axisY1. In the example of the fins 5 shown in FIGS. 9 and 10, twelve finsare provided on the inner circumferential surface 1 d of the outer tube1. In the example of the fins 5 shown in FIG. 9, they are arrangedaround the axis Y1 at angular intervals that are obtained by dividing360° by twelve, i.e., arranged at intervals of 30°.

Note that the nozzle structure 30 comprises the fins 5, and the fins 5guide the hydrogen gas blown out from the hydrogen gas blowing duct 3 bso that the hydrogen gas is further propelled in a direction roughlyparallel to the axis Y1 toward the one end part 1 b of the outer tube 1.Further, the fins 5 prevent the hydrogen gas from flowing in such amanner that it is rotated around the axis Y1. Therefore, the progress ofthe mixture of the hydrogen gas and the oxygen-containing gas is furthersuppressed. Consequently, it is possible to further prevent thetemperature of the tubular flame F1 from locally becoming high andthereby to further reduce the amount of generated NOx.

EXAMPLE

Next, a combustion experiment was carried out by using an example of thenozzle structure 10 (see FIGS. 1 to 3), and results of measurement inwhich amounts of generated NOx were measured for different combustionload factors are explained.

Note that in a comparative example 1, a combustion experiment wascarried out by using a publicly-known nozzle structure having aconfiguration different from that of the nozzle structure 10 and byusing a hydrocarbon gas as a fuel gas. This known nozzle structure iscommonly used in cases where a hydrocarbon gas is used as a fuel gas. Ina comparative example 2, a combustion experiment was carried out byusing a publicly-known nozzle structure having a configuration differentfrom that of the nozzle structure 10 and by using a hydrogen gas as afuel gas. In each of the comparative examples 1 and 2, amounts ofgenerated NOx were measured for different combustion load factors.

As shown in FIG. 11, in the example, the amount of generated NOx tendsto be constant even when the combustion load factor is increased. Incontrast to this, in the comparative examples 1 and 2, the amount ofgenerated NOx tends to increase when the combustion load factor isincreased. The amounts of generated NOx in both of the comparativeexamples 1 and 2 were higher than the amount of generated NOx in theexample irrespective of the combustion load factor. In other words, theamount of generated NOx in the example was lower than those in thecomparative examples 1 and 2.

Note that the present disclosure is not limited to the above-describedembodiments and they can be modified as desired without departing fromthe spirit of the present disclosure. For example, although the nozzlestructures 20 and 30 (see FIGS. 7 to 10) are equipped with the fins 4and 5, respectively, they may be equipped with either of the fins 4 and5.

From the disclosure thus described, it will be obvious that theembodiments of the disclosure may be varied in many ways. Suchvariations are not to be regarded as a departure from the spirit andscope of the disclosure, and all such modifications as would be obviousto one skilled in the art are intended for inclusion within the scope ofthe following claims.

What is claimed is:
 1. A nozzle structure for a hydrogen gas burnerapparatus, comprising an outer tube and an inner tube concentricallydisposed inside the outer tube, wherein the inner tube is disposed sothat an oxygen-containing gas is discharged from an opened end of theinner tube in an axial direction, and the outer tube extends beyond theopened end of the inner tube in the axial direction so that a hydrogengas passes through a space between an inner circumferential surface ofthe outer tube and an outer circumferential surface of the inner tubeand proceeds along an outer periphery of the oxygen-containing gas,thereby suppressing contact between and mixture of the oxygen-containinggas and the hydrogen gas, wherein the oxygen-containing gas is air, anda ratio Va/Vh between an air flow velocity Va and a hydrogen flowvelocity Vh is in a range of greater than or equal to 0.1 and less thanor equal to 3.0.
 2. The nozzle structure for a hydrogen gas burnerapparatus according to claim 1, further comprising: an oxygen-containinggas blowing duct configured to blow out the oxygen-containing gas in theaxial direction and make the oxygen-containing gas pass through a spaceinside the inner tube; and a hydrogen gas blowing duct configured toblow out the hydrogen gas into the space between the innercircumferential surface of the outer tube and the outer circumferentialsurface of the inner tube in the axial direction, and make the hydrogengas pass through between the inner circumferential surface of the outertube and the outer circumferential surface of the inner tube, whereinthe oxygen-containing gas blowing duct has a circular shape, and thehydrogen gas blowing duct has an annular shape so as to surround theoxygen-containing gas blowing duct.
 3. The nozzle structure for ahydrogen gas burner apparatus according to claim 1, wherein in a sectionbetween the opened end of the inner tube and a base part thereof, a finthat extends in the axial direction while protruding toward the innertube is provided on the inner circumferential surface of the outer tube,or a fin that extends in the axial direction while protruding toward theouter tube is provided on the outer circumferential surface of the innertube.
 4. The nozzle structure for a hydrogen gas burner apparatusaccording to claim 1, wherein the ratio Va/Vh is substantially 1.0.